Texas Waste Water Treatment Ch#03 Composition and Characteristics

Community wastewater consists of wastewater from domestic, industrial, and commercial facilities. Surface runoff and groundwater may add to the flow. As community activity changes, the chemical, biological, and physical qualities of the wastewater also change. NOTE: Also because it is so very much more repellant than tide pods......

Raw waste water quantity varies from 40 gallons to 280 gallons per person per day. An average of 100 gallons per person per day is used in designing collection and treatment plants when more reliable data is not available. The Biochemical Oxygen Demand(BOD) or the amount of oxygen used by the microorganisms in raw domestic wastewater varies from 100 to 300 mg/L. Assuming 200 mg/L about 0.17 pounds of BOD are contributed daily by each person (this is called the BOD population equivalent).

Septic wastewater is a dark color, has a disagreeable odor, and contains no DO. The floating material is hard to see, and gas bubbles are seen rising to the surface. The change from fresh to septic is caused by bacterial action, as anaerobic bacteria consume organic materials and produce organic acids and odorous gases.

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Solids in wastewater are classified as follows: • Total (TR) • Total suspended solids (TSS or SS) • Total dissolved solids (TDS) • Settleable solids (SS) • Non-settleable solids • Floatable solids • Volatile suspended solids (VSS) • Inorganic solids (ash or fixed) • Organic matter (volatile)

Organic compounds contain carbon along with other elements, usually oxygen and hydrogen. These organics are of animal or vegetable origin and include fibers, oils, fats, starches, sugars, and proteins. Aerobic treatment stabilizes proteins to carbon dioxide, water, nitrate, sulfate, and phosphate.

Organic compounds contain carbon along with other elements, usually oxygen and hydrogen. These organics are of animal or vegetable origin and include fibers, oils, fats, starches, sugars, and proteins.

Carbohydrates include sugars, starches, and cellulose and range in size from simple sugars to high molecular weight cellulose.

Biochemical oxygen demand (BOD, or specifically BOD5 when referring to the test) is the quantity of dissolved oxygen, expressed as milligrams per liter, required (depleted or used up) to partially stabilize the decomposable organic matter in a waste stream by chemical and biological action over 5 day period of time at 20°C.

For domestic wastewater that does not contain excessive toxic or inhibitory materials, the BOD test represents the “strength” of the wastewater. A sample is considered “strong” if it has a high organic content and a high BOD. If strong wastewater or untreated waste is discharged into a receiving stream, bacteria will begin to break down the organic matter. In the process, bacteria use DO in the stream. Algae masses in streams will also consume DO during the night.

Chemical oxygen demand (COD) is another way to determine the amount of oxidizable organic matter in wastewater. The COD test uses strong chemical oxidation rather than the microbial action associated with BOD. COD values are higher than BOD because the COD test represents a more complete chemical oxidation of the organic matter. COD testing requires 2–4 hours. COD values for a raw domestic waste generally will range from 200 to 750 mg/L. For domestic wastewater, the ratio of the COD test result to the BOD5 test result on the same sample is usually about 2.5 to 1.0. Industrial waste contributions may increase the COD value to five or more times the BOD value.

Methane combusts, carbon dioxide displaces oxygen, hydrogen sulfide deadens the sense of smell and is corrosive when mixed with water.

Pathogenic bacteria cause intestinal disorders and fever. They are found in the intestines of humans and other warm-blooded animals. Pathogenic bacteria carried by unsafe water and wastewater cause diseases such as typhoid, paratyphoid, dysentery, cholera, and others. Pathogenic bacteria are destroyed by proper disinfection of wastewater effluents.

To understand how the wastewater treatment process works, one must know the cycles of decay in organic decomposition. Matter can neither be created nor destroyed, but may change from one form to another in the natural process of the life-and-death cycle. This change is evident in the wastewater treatment process. The cycles of decay include the nitrogen cycle, sulfur cycle, and carbon cycle.

The amount of wastewater flowing through a treatment plant varies with the time of day, the seasons, and the weather. It is important to monitor the flow in order to calculate the load on the plant as well as to determine inflow/infiltration, treatment cost, and flow trends. As communities grow, so do wastewater treatment needs. If wastewater flow trends are monitored, future treatment needs can be projected and met. Any plant with a design flow above 0.5 MGD is required to install instrumentation for continuous flow totalizing.